1. Field of the Invention
The present invention relates to nanostructures, and more particularly to a system and method of electrically induced breakdown of nanotube nanostructures.
2. Description of Related Art
In the field of molecular nanoelectronics, few materials show as much promise as nanotubes, and in particular carbon nanotubes, which comprise hollow cylinders of graphite, angstroms in diameter. Nanotubes can be made into tiny electronic devices such as diodes and transistors, depending on the nanotube""s electrical characteristics. Nanotubes are unique for their size, shape, and physical properties. Structurally a carbon nanotube resembles a hexagonal lattice of carbon rolled into a cylinder.
Besides exhibiting intriguing quantum behaviors at low temperature, carbon nanotubes exhibit at least two important characteristics: a nanotube can be either metallic or semiconductor depending on its chirality (i.e., conformational geometry). Metallic nanotubes can carry extremely large current densities with constant resistivity. Semiconducting nanotubes can be electrically switched on and off as field-effect transistors (FETs). The two types may be covalently joined (sharing electrons). These characteristics point to nanotubes as excellent materials for making nanometer-sized semiconductor circuits.
Current methods of studying nanotubes rely on the random formation of both metallic and semiconducting nanotubes. There is no known method for reliably preparing a nanotube having particular characteristics, much less for preparing nanotubes to exhibit junctional behavior such as transistors, diodes, etc. Nor are there known methods of nanotube separation by selective synthesis or post-synthesis which have proven to have any measurable level of success. Heretofore, nanotubes must have either been individually separated from mixtures of metallic and semiconducting nanotubes or randomly placed over an electrode to be studied. However, there is no observable consistency in such methods.
This lack of control, compounded by nanotubes"" tendency to bundle together, has hindered the study of nanotube physics and is seen as a primary roadblock in the nanotube development including nanotube-based electronic technology. Therefore, a need exists for a system and method of preparing nanotubes having desired characteristics.
The present invention relates to a method for forming a device comprising the steps of, providing a substrate, providing nanotubes in contact with the substrate, and selectively breaking a nanotube using an electrical current. The method further includes the step of depleting a semiconducting nanotube of carriers.
Depleting a semiconducting nanotube of carriers further includes the step of applying a voltage to a gate electrode. The method includes applying the electrical current through the nanotube from a source electrode to a drain electrode.
The nanotubes include multi-walled nanotubes including metallic and semiconducting nanotubes. The nanotube can have an outer metallic nanotube that is broken.
The nanotubes include single-walled nanotube ropes including metallic and semiconducting nanotubes. At least one metallic nanotube is broken.
The nanotubes are provided at a density between a monolayer and about {fraction (1/10)}th of one percent coverage. The substrate is an insulator and includes an array of metallic pads. The substrate is silica based and includes the array of metallic pads. Each pad includes one of a source electrode, a drain electrode, and a gate electrode.
Providing a substrate is accomplished using lithography to form an array of pads, each pad including a corresponding electrode, on an insulating substrate.
The nanotubes are carbon nanotubes. The method also breaks stray nanotubes.
According to an embodiment of the present invention, a method of modifying at least one characteristic of a nanotube is provided. The method includes providing a mixture of nanotubes, and applying a current to the mixture, inducing the selective breakdown of the nanotube mixture. The method further includes removing carriers from a semiconducting nanotube.
The current selectively breaks metallic nanotubes. A power applied to the mixture is about 500 xcexcW.
The nanotube is one of a multi-walled nanotube and a single-walled nanotube rope. The characteristic is one of diameter, density, and conductance. The mixture includes metallic and semiconducting nanotubes. The current density is greater than 109 A/cm2.
According to an embodiment of the present invention, a method is provided for forming a device. The method provides an insulating substrate including a source electrode, a drain electrode, and a gate electrode. The method provides carbon nanotube bundles including metallic and semiconducting component nanotubes in contact with the substrate, wherein the nanotubes are provided at a density of about one percent coverage. The method applies a voltage to the gate electrode to deplete the semiconducting component nanotubes of carriers, applies an electrical current through the nanotube, from a source electrode to a drain electrode, and breaks at least one metallic component nanotube to form a field effect transistor. The carbon nanotube bundle can be a multi-walled nanotube or a single-walled nanotube rope.